The Reserve Bank also warned that the high New Zealand dollar was not "sustainable".

The kiwi rose against the US dollar after the announcement, moving from US85.83c at 8.59am to a high of US86.18c before quickly settling back down to about US86c.

In a one-page statement explaining the rate hike, the bank said that to keep inflation in check, rates would need to rise "towards a level at which they are no longer adding to demand".

That means interest rates would neither push the economy ahead nor hold it back - a "neutral" rate seen by economists as about 4.5 per cent.

The bank has previously warned that official interest rates could rise about 200 basis points over the next couple of years, pushing mortgage rates to about 8 per cent.

Some economists had said that with annual inflation remaining so low, at 1.5 per cent in figures out last week, and such a high dollar, the Reserve Bank might take a pause with rate rises later in the year.

Wheeler said today the speed and extent of future rate rises would depend on economic data and the bank's assessment of inflation, including how much the high dollar would hold down inflation.

The next announcement on interest rates is due on June 12.

Headline inflation was now "moderate", but inflation pressures were increasing and were expected to continue over the next two years, so it was important to keep expectations of price rises "contained".

The economy had gained a head of steam, growing about 3.5 per cent in the year to March. Prices for New Zealand export commodities remained "very high", though auction prices for dairy products had fallen 20 per cent in recent months, the bank said.

The five-year run of extremely low interest rates and strong growth in building were supporting the economic recovery.

Strong net migration was rising, which was boosting housing and consumer demand.

Official figures out yesterday showed a net migration gain of about 32,000 in the March year, with economists predicting that to move close to 40,000 by the end of the year.